×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Voltage Range K Factor understanding
2

Voltage Range K Factor understanding

Voltage Range K Factor understanding

(OP)
Hello all. I am trying to gain a better grasp of K-factor as associated with breakers and MCCs. It was mentioned to me by an associate that he had 15kV equipment being operated at 6.9kV so the K-factor would affect the short-circuit current available. This is a new subject to me so I am hoping someone can help with links to good sources or advice. Thanks.

RE: Voltage Range K Factor understanding

K-factor, as I know it, has more to do with transformers and distorted waveforms. Are you sure you friend doesn't bull?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Voltage Range K Factor understanding

Skogsgurra, there was a k-factor (different from transformer k-factor) in an obsolete IEEE/ANSI breaker standard.  It has been gone for quite some time and I don't know enough of the details to answer the original question, but it is a legitimate question.

RE: Voltage Range K Factor understanding

The ANSI C37 K-factor provides a range of adjustment of short-circuit rating based on the ratio of the actual voltage to the maximum rated voltage of the breaker.  So if a K-rated 15 kV breaker is applied at a lower voltage, such as 6900 V, there will be an increase in short circuit interrupting capability - up to a point defined by the K-factor.  

New ANSI standards no longer use the K-factor, but it would still apply to any breakers tested and rated by that method.  

As mentioned, this is unrelated to Transformer K-rating.  

RE: Voltage Range K Factor understanding

(OP)
dpc,

Thanks! I think I understand it now with your and davidbeach's feedback.

RE: Voltage Range K Factor understanding

And I learned something, too!

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Voltage Range K Factor understanding

dpc:

Although you've said it (k-factor) is not included in the new ANSI-standards, does some American switchgear manufacturers still use it?

Never heard of it (in the breaker-world) before.

Thanks
Regards
Ralph

Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376: Eng-Tips.com Forum Policies

RE: Voltage Range K Factor understanding

Here's my understanding.

K factor was for air and oil based circuit breakers with interrupting ratings given in short circuit MVA.  As the operating voltage decreased, the short circuit current capability increased up to some maximum value given by the K factor. The interrupting MVA was constant down to some minimum voltage so the current value could be increased.

Oil and Air Blast circuit breakers could  dissipate a given amount of arc energy. The interrupting current levels were not the limiting factor. The arc energy was the limit.

SF6 and vacuum interrupters use a different arc interruption phenomenon.  They are limited by the current and not the arc energy.  Their interrupting rating does not increase as the application voltage level drops.  K=1.0

See Powell Electric’s website for a good white paper on this.  

http://www.powellind.com/main/Uploadpdf/ptb%2046%20significance%20of%20k%20factor%20in%20circuit%20breaker%20ratings.pdf

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources